Latex particles obtained by emulsion polymerization can have a variety of applications, including for use as model colloids for calibration of instruments used to measure particle size, for immobilization of biomolecules (such as proteins or peptides) on the surface of the particles, for development of new types of immunoassays, and for film formation for ink-jet printing, painting, and coating applications. While latex particulates have applications in these and other fields, the ink-jet ink imaging application can be used to favorably illustrate latex properties. Specifically, there has been great improvement in the area of water durability of ink-jet inks through incorporation of certain ink-jet compatible latex polymers. When printed as part of an ink-jet ink, a latex component of the ink can form a film on a media surface, entrapping and protecting the colorant within the hydrophobic print film.
This being said, while latex particulates can improve durability of prints, they often exhibit undesirable qualities while in suspension. Water soluble polymers can increase the viscosity of a suspension because of dissolution. When the suspension is an ink, the viscosity can affect printability. Particularly, higher viscosity inks do not print properly in certain architecture. Further, if it is possible to print the ink, water soluble polymers in the printed ink can reduce the overall printed image durability. To overcome these drawbacks, water insoluble latex particulates can be added to a suspension. The addition of this type of latex particulates often only increase the viscosity of the suspension, e.g. ink, very slightly compared to the addition of water soluble polymers, and can therefore be more desirable for use. Regardless of the type of latex particles used, these latex particulates can have drawbacks. For example, they tend to settle out of and/or agglomerate in suspensions over time, and therefore, often are not stable in many storage conditions.
Latex particulates can be prepared through conventional emulsion polymerization processes. In this method, hydrophobic monomers are emulsified in water. Free-radical initiators have been used to initiate the polymerization. In some systems, the hydrophobic monomers are emulsified along with added surfactant, which can be adsorbed on the surface of the latex particulates. Unfortunately, this surfactant adsorption does not greatly increase particulate stability under many ink-jetting conditions that include the use of high-shear. This is particularly the case with thermal ink-jetting systems. An alternate approach is to include reactive surfactants in an attempt that they be included along with the monomers in the polymer chain. This approach can also be undesirable, as the surfactants do not get incorporated into the latex particulate fully because of the low reactivity of the surfactant compared to other monomers. Furthermore, incorporation of these surfactants occurs in a more random manner and not all particulates necessarily include appropriate amounts of the surfactant. Furthermore, the particle size of the latex particulate is affected because of the random substitution of surfactant along the chain length of the polymer. This being the case, there is a continued need to provide improved latex particulates and methods of preparing the same.